A pressure vessel for storing a fluid medium (such as hydrogen) typically includes a pressure chamber which contains the pressurized fluid medium that is moved in a controlled manner in or out of the vessel. In certain designs, the pressure vessel includes an inner plastic liner with two metal mouthpieces (bosses) arranged on opposite ends, and a filament wound outer shell to support the inner vessel liner.
Typically, the vessel liner is manufactured using a conventional injection molding, blow molding, rotational molding process, or thermoforming process. For example, the following patent documents describe a vessel liner (WO 19991039896 Dulisse, JMK; WO 2007/079971 Müller, Xperion; DE 19526154 Lange, Mannesmann etc.; and WO 1999/013263 Jensen, Raufoss), each of which is incorporated herein by reference in its entirety.
To permit controlled movement of fluids in or out of the pressure chamber, the vessel is typically configured with a pressure chamber orifice and a boss is fitted in the orifice. The boss is threaded or otherwise shaped for connection to nozzles, valves, gauges, tubes, and similar fixtures which direct and control fluid flow. Accordingly, the boss is formed of a metal or another conventional material having desired properties.
The boss typically includes a cylindrical neck with a longitudinal passage that provides fluid communication between the pressure chamber and the environment outside the vessel. In certain designs, the boss includes a shoulder portion secured to one end of the neck. The shoulder portion, which is larger than the pressure chamber orifice, is secured to the liner of the pressure vessel to militate against relative movement between the boss and the liner.
In certain applications, the pressure vessel includes an end cap. Typically, the end cap is coupled to the vessel liner using a welding procedure. As such, the end cap is designed to receive and secure the boss or other utility device to the pressure vessel.
In application, it is important to provide a proper coupling surface between the end cap and the vessel liner. Additionally, it is important to provide a smooth outer surface on the vessel liner of the pressure vessel to maximize the performance of a composite winding. Further, both the vessel liner and the end cap need to meet certain permeation requirements to minimize leakage of the stored fluid from the pressure vessel. Currently, the materials used to meet permeation requirements are not suitable for providing a proper outside surface to maximize the performance of a composite winding. Likewise, the materials typically used to produce a smooth outer surface on the vessel liner may not provide suitable permeability for particular fluids stored in the pressure vessel.
It would be desirable to develop a pressure vessel and a method for producing the pressure vessel, wherein the pressure vessel and method provide a proper coupling surface between a vessel liner and an end cap, a substantially smooth outer surface of the pressure vessel, and a suitable permeability for storing various pressurized fluids.